The present invention especially refers to a shaft driving device for driving a plurality of heald shafts arranged in parallel, said shaft driving device comprising respective shaft raising elements each associated with a heald shaft and provided with a linkage and a plurality of lever elements connecting the linkage to the respective heald shaft, and further comprising drive means which are arranged on opposite front sides of the heald shafts, alternate said drive means on opposite sides being drivingly connected to those ends of juxtaposed shaft raising elements which face said drive means.
Such a shaft driving device according to the prior art is shown in FIG. 4A. The shaft driving device 400 is designed for driving a plurality of heald shafts 410 and 410', two respective ones of said heald shafts 410 and 410' being shown in FIG. 4A. In said heald shafts one heald or a plurality of healds 412 and 412' are provided for heddling warp threads. By heddling warp threads in the plurality of heald shafts and by a suitable position of the individual heald shafts relative to one another, it will be possible to open, in the manner known, a weaving shed into which weft threads can be woven with the aid of suitable means.
In this known device, each heald shaft 410 is driven via a respective shaft raising element in a driving direction 411 by a respective drive means 450, which is provided on the left front side of the heald shaft arrangement according to FIG. 4A.
Each shaft raising element comprises a linkage 420 which is connected to the heald shaft 410 by means of a plurality of lever elements 430. Each linkage 420 is provided in the form of a connecting rod having an approximately uniform cross-section.
The heald shafts 410' are driven via a suitable mechanism with the aid of a drive means 450', i.e. each of said heald shafts is driven via a shaft raising element provided with a linkage 420' connected to the heald shaft 410' by means of a plurality of lever elements 430'. The drive means 450' for the heald shafts 410' are provided on the right front side of the heald shaft arrangement.
FIG. 4A additionally shows, under the connecting rod of the linkage 420 of the first shaft raising element, the pulling and pushing forces 470 acting on respective points of the connecting rod while the first heald shaft is being driven.
As can be seen from FIG. 4A, this force is highest on the side facing the drive means 450. The force required for moving all the lever elements 430 must there be taken up by the connecting rod. After each lever element, this force acting on the connecting rod of the linkage 420 is reduced by the amount required for driving the lever element 430 in question.
In order to enable the connecting rods 420 and 420' to take up the above-described pushing and pulling forces when the respective heald shafts are being driven, each connecting rod must be implemented such that it is rigid and buckle-proof depending on the forces occurring. Hence, the lever elements must have at least certain minimum cross-sectional dimensions in the direction of the neighbouring shaft raising element.
Especially in the case of looms for weaving wide fabrics and looms for weaving industrial fabrics, in which high pressing and pulling forces occur, this requirement will, however, result in comparatively large cross-sectional dimensions (cf. FIG. 4B) of the connecting rods in the direction of the neighboring shaft raising element.
FIG. 4B shows a sectional view along line IV--IV in FIG. 4A. In this sectional view, the four linkages 420 and 420' of the shaft raising elements and the heald shafts 410 and 410' associated therewith are shown. In addition, the healds 412 and 412' for heddling the warp threads are shown in this figure.
Furthermore, the distance between the heald shafts 410 and 410' of two neighboring shaft raising elements is designated by reference numeral 413 and the distance between the linkages 420, 420' in the direction of the neighboring shaft raising element is designated by reference numeral 425.
As can additionally be seen from FIG. 4B, also the minimum distance 413 between the healds 412, 412' of neighboring heald shafts 410, 410' is given by the cross-sectional dimensions, which are predetermined by the force applied to the linkage 420 by the respective drive means 450 in the direction of the neighboring shaft raising element. It follows that, in view of comparatively large cross-sectional dimensions, also a comparatively large minimum distance between the heald shafts 410 and 410' is also obtained.
This comparatively large distance 413 between neighboring heald shafts 410 and 410' makes it necessary that especially the rear heald shafts must carry out a comparatively large lifting motion for opening a weaving shed.
This comparatively large lifting motion has, in turn, the effect that the force required for driving the heald shafts 410, 410' must be very large and that the connecting rods of the linkages 420, 420' must be provided with correspondingly large cross-sectional dimensions.
In view of these disadvantages of the prior art, it is the object of the present invention to improve a shaft driving device in such a way that the above-described disadvantages can be avoided.